Our overall goal is to understand the host immune response to vaccination with soluble recombinant HIV-1 Envelope immunogens in non-human primates (NHP), with the aim of developing Envelope-based vaccines that can elicit broadly neutralizing antibodies. 20-30% of HIV-1-infected subjects develop broadly neutralizing antibodies (bNAbs) within the first three years after infection, given sufficient antigenic stimulation from replicating virus and proper CD4+ T cell help. Even in an environment of HIV-related immune dysregulation, this subset of subjects is able to successfully produce bNAbs, providing hope that this can be accomplished by vaccination in healthy subjects. Currently it is not understood why Env-based vaccines have failed to elicit bNAbs in both NHP and humans, despite displaying the conserved epitopes of some of the most broadly neutralizing anti-HIV-1 antibodies known. It is possible that B Cell Receptors (BCRs) similar to those of known bNAbs are not stimulated by vaccination with recombinant Env immunogens or that they become activated, but do not receive sufficient stimulation by vaccination to mature into bNAbs. This application aims to resolve a significant gap in our fundamental understanding of why the current generation of gp140 Env immunogens has failed to elicit bNAbs by following the stimulation and maturation of B cell receptors during vaccination with clade C gp140 immunogens.